1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light [herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays, gamma-rays and the like].
2. Description of the Prior Arts
Photoconductive materials, which constitute solid image pick-up devices, or image forming members for electrophotography and manuscript reading apparatuses in the field of image formation, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/Dark current (I.sub.d)], spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value and no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as an office business machine, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon [hereinafter referred to as "a-Si"] has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German Laid-Open Patent Publication No. 2933411 discloses an application of a-Si for use in a photoelectric transducer reading device.
However, under the present situation, the photoconductive members having photoconductive layers constituted of a-Si of the prior art are required to be improved with respect to combined characteristics, including various electrical, optical and photoconductive characteristics such as dark resistance value, photoconductivity and response to light, environmental characteristics in use such as humidity resistance, and further stability with lapse of time.
For instance, when the a-Si photoconductive member is applied to an image forming member of an electrophotographic device, residual potential is frequently observed to remain during use thereof. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigues by repeated uses, so called ghost phenomenon resulting from the accumulation of fatigues wherein residual images are formed, and the like.
Further, according to the experience by the present inventors from a number of experiments, a-Si materials constituting the photoconductive layer of an image forming member for electrophotography have a number of advantages, as compared with inorganic photoconductive materails such as Se, CdS, ZnO and the like or organic photoconductive materials such as PVCz, TNF and the like of the prior art, but it is also found that they have several problems to be solved. Namely, when charging treatment is applied, for formation of electrostatic images, to the photoconductive layer of an image forming member for electrophotography having a photoconductive member constituted of a mono-layer of a-Si which has been endowed with characteristics for use in a solar battery of the prior art, dark decay is markedly rapid, whereby it is difficult to apply a conventional electrophotographic method. This tendency is further pronounced under a humid atmosphere to such an extent, in some cases, that charge can not be retained at all until development.
Further, a-Si materials may contain, as constituent atoms, hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, and the like, for improving their electrical and photoconductive characteristics, boron atoms, phosphorus atoms, and the like, for controlling the electroconduction type, and other atoms for improving other characteristics. Depending on the manner in which these constituent atoms are contained, there may be caused problems sometimes with respect to mechanical characteristics after layer formation.
That is, for example, in the case of an image forming member for electrophotography, an a-Si layer is formed on a cylindrical support made of a metallic material such as aluminum, and the like. Due to its large strain characteristic, there will frequently occur inconveniences such as formation of cracks in the layer, loosening of the layer from on the support or peel-off of the layer as a whole, although the problems may depend on the conditions for preparation of the layer.
Further, an ordinary a-Si layer per se does not generally exhibit good characteristic with respect to adhesion to a support made of a metallic material such as aluminum and the like and therefore there is a problem in the characteristic of repeated uses for a long term. There is also a problem that good electrical contact can be formed with difficulty between the support and the a-Si layer, and further it is subjected to change with lapse of time.
Thus, it is desired in designing a photoconductive material to make efforts to obtain desirable electrical and photoconductive characteristics along with the improvement in a-Si materials per se.